בשקופית 14 של הרצאה 5 מוצג החלק של הcleanup באלגוריתם המעבר מCFG לCNF.
מהשקופית -
- for each rule with A on LHS, make sure that A appears on RHS of some
rule that is reachable from start variable.
- for each rule with A on RHS, make sure that A also appears on LHS of a
rule

"Make sure" means that if there is a rule of the form "A -> " but you cannot reach A (that is, it does not appear on the RHS of any other rule), you can delete this rule.
The same goes for the other guidelines.
It doesn't mean there has been a mistake or that the CFG is "wrong" - it simply means that there are unreachable rules.